Marshall JMP 1992 Super Bass 100 Watt Amp Head (1970)

Just into the shop is perhaps one of the coolest vintage Marshalls we've ever had in the building - a 1970 Marshall JMP 1992 Super Bass 100 amplifier. Long heralded as one of the greatest high powered guitar amplifiers of the 20th Century, the Super Bass 100 arrived on the scene in 1967, primarily offered a bass amplifier. Guitarists quickly caught onto the reality that the Super Bass made for a great guitar amplifier, providing a smoother, fuller option when compared to the Super Lead model made available at the time.

This particular amp bears the markings and schematic of the "Gen 2" Super Bass, featuring a quartet of Svetlana EL34 power tubes as opposed to the previous KT66 and 6550 loaded predecessors. The manufacturing chart notes a date of '11-2-70' and also features its original Dagnall transformers throughout. At one point the amplifier's circuit had been slightly modified, but was recently returned to its stock circuitry, and frankly sounds amazing!

Clean tones are big, lush, and deep, with chest-thumping power even at lower volumes. Both Normal and Bright channels offer up their own flavor, and using the popular "jumpering" technique, you can blend in a mix of those two channels to fine tune your sound. The amplifier begins to break up around 12:00 and continues to progress into smooth, punchy overdrive with impressive power.

While we would consider the overall condition to be Very Good, there are a few particular changes of note that are worth mentioning. The most obvious is the replacement back panel, which is a more generic thin-ply replacement painted black. Second, previous work done on the amp shows the use of a penny to cover up a preamp tube chassis hole (the hole itself is factory, but the penny certainly is not!). The original speaker impedance selector switch was also replaced and now uses a knob to select through the ohm settings. The voltage selector was also disengaged to only allow operation at 120v. Lastly, a modern Marshall badge replaced the original, seemingly some time ago.

The good news? Transformers and pots along with the main PTP board are original to the amplifier, and no additional holes have been found on the chassis. The amp received its most recent service by way of Boston-area amp tech Stan Day, who completed the work in November 2022. The amp is fully serviced and ready to rock.

With a bevy of low/mid powered 1x12 combos here at the shop, this 100 watt powerhouse of a vintage Marshall proves to all of us why these amps are so highly desired. The feel of a high-powered amp like this never seems to go out of style.